This invention generally relates to exercise equipment and in particular to exercise treadmills having an AC motor control system.
Exercise treadmills are widely used for performing walking or running aerobic-type exercise while the user remains in a relatively stationary position. In addition exercise treadmills are used for diagnostic and therapeutic purposes. Generally, for all of these purposes, the person on the treadmill performs an exercise routine at a relatively steady and continuous level of physical activity. One example of such a treadmill is provided in U.S. Pat. No. 5,752, 897.
Although exercise treadmills that use an AC motor to drive the belt have reached a relatively high state of development, they still have a number of problems involving treadmill frame resonance or vibration, low speed operation and power consumption.
It is therefore an object of the invention to provide an exercise treadmill having improved AC motor control.
An additional object of the invention is to shift the phase relationship of a three phase drive signal applied by the motor controller to the motor in order to minimize frame resonance.
Still another object of the invention is to provide a method to minimize frame resonance by staggering the phase relationship of the three phase drive signal applied by the motor controller to the motor.
A further object of the invention is to overcome operational problems of a three phase induction motor at low speed. By commanding the motor controller to present a drive signal of a frequency much higher than the desired motor speed to the motor at low speeds, a high slip, or difference between the driving signals circulating field and the actual motor speed, will result thereby improving low speed performance of the treadmill.